Devices for generating and dispensing foams by manual compression of a reservoir or bulb are well known. The compression typically forces air and foamable liquid from a reservoir into a mixing chamber where they mix to produce a foam before being dispensed from the device. Such devices are disclosed in a series of patents issued to H. Earl Wright: U.S. Pat. No. 3,428,222, issued Feb. 18, 1969; U.S. Pat. No. 3,709,437, issued Jan. 9, 1973; U.S. Pat. No. 3,937,364, issued Feb. 10, 1976; U.S. Pat. No. 4,018,364, issued Apr. 19, 1977; U.S. Pat. No. 4,184,615, issued Jan. 22, 1980; U.S. Pat. No. 4,531,659, issued Jul. 30, 1985; and U.S. Pat. No. 4,880,161, issued Nov. 14, 1989, each of which is incorporated by reference.
Most prior art foaming devices, including those disclosed in the Wright patents, share a number of common elements. Typically, each foamer contains a liquid reservoir for storing the foamable liquid. Each contains a compressible air supplying means. Each contains a mixing chamber where the foamable liquid and air mix to form the foam. Each contains a restricted passage from the air supplying means to the mixing chamber. Each contains a passage from the liquid reservoir to the mixing chamber, typically a vertical dip tube. And each contains some means for dispensing foam from the mixing chamber. As mentioned above, these foamers are all operated by compressing the air supplying means which forces air and foamable liquid into the mixing chamber. When the air supplying means is released, the vacuum created thereby draws foam from within the device back into the liquid reservoir.
The ratio of foamable liquid to air supplied to the mixing chamber is critical in foam formation in these devices. If the ratio is too high, the foam is too wet. If the ratio is too low, the foam is too dry. While the various Wright foamers are designed to maintain a fairly constant liquid-to-air ratio when compressed periodically, these foamers, and others known in the art, suffer from an alteration in the ratio with rapid, repeated usage. This feature can be visualized by reference to FIG. 3 of Wright, U.S. Pat. No. 3,709,437. Upon an initial compression of the reservoir, air flows through air passages 58, liquid flows through tubular member 38, and the two meet in the mixing chamber 42 where the foam is formed. When the reservoir is released, the ball check valve 60 seats and foam flows back through air passages 58. If the reservoir is immediately re-compressed, foam dripping down from the air passages will be forced back into the mixing chamber. The addition of foam through the air passages to the mixing chamber, rather than pure air, increases the ratio of liquid to air and results in the formation of an overly wet foam. Accordingly, there is a need for a foamer which maintains a constant liquid to air ratio during rapid, repeated usage.